The growing demand for sensors in industry, medicine, environmental monitoring, and even in our own homes, drives the efforts to develop increasingly sensitive techniques to detect biomarkers in extremely low concentrations. For example, reliable laboratory diagnosis has been one of the foremost priorities for promoting public health interventions. For this, a standard clinical verification method is ELISA [1]. Here a color change reaction of enzyme-labeled antibodies takes place, which enables the detection of extremely low concentrations. However, ELISA is rather slow, and the reaction kinetics cannot be tracked. An alternative optical biosensing method is surface plasmon resonance (SPR) that has evolved to be the standard approach among various label-free optical methods [2]. Biosensors do not require that any material be multiplied to generate a signal, or that the biological sample go through multiple lab processing steps. However, the resonance exploited in plasmon-based sensing is governed by the optical properties of the metal film used. This results in a lack of flexibility in the operation wavelength. Furthermore, the resonance width is determined by the metal losses and cannot be narrowed to lower the limit of detection. Many scientists and engineers have put vast efforts into developing optical fibers, which made it a practical communication medium and changed the world. Nowadays, optical fibers connect the globe via internet, which is currently the backbone of our information-driven society and economy. Large-scale applications, not only in telecommunication [3], but also in sensing applications due to their multiple advantages compared to conventional electric sensors [4,5], becoming increasingly important for applications in industrial process and quality control, biomedical analysis, and environmental monitoring [6–9]. Fiber optics research has regained substantial interest during recent years by the integration of materials that are traditionally not used in fiber optics [10-12]. The combination of fiber–optic-based platforms with the nanotechnologies is opening the opportunity for the development of high-performance photonic devices. The generation of optical resonances by means of the deposition of dielectric nanofilms on special optical fiber allows measuring precisely and accurately surface refractive index changes. This approach enhances the light-matter interaction in a strong way, thus turning out to be more sensitive compared to other optical technology platforms. In this project, we propose to use a new type of resonance in optical fiber, the electromagnetic surface wave resonance (ESW) propagating at the interface of two dielectric media, different from those reported in optical fibers (SPR and lossy mode resonance), for the development of biosensors. ESW-based optical biosensors represent the most advanced and developed optical label-free biosensor technology [13]. The most popular ESW-based sensing technology is SPR. Due to the fact that plasmons are excited at wavelengths where metals offer strong dispersion [14], SPR sensors can achieve high sensitivities. However, along with strong dispersion, absorption is unavoidable in metallic components, producing undesirable broadening of the resonance, thereby posing an upper bound to the overall figure of merit (FOM) [13]. On the other side, purely dielectric interface ESW biosensors have several advantages that make them even more attractive. Because the dielectrics employed at the interface are characterized by much lower extinction coefficients than metals, ESW resonances appear much narrower than those observed for SPR. Furthermore, they are inherently inert with respect to sensitive biological materials. Here we consider structures based on geometrically modified optical fiber with a structure of purely dielectric materials deposited on its surface, seeking to develop an affordable and low-cost platform.